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Sample Transport
On-line techniques have the disadvantage that the sample needs to be flowing to the analyser. All wetted parts have the risk to foul resulting in blocking the pipes after a while. General rules to overcome problems are:
- Try to keep the distance between analyser and sample take of point as short as possible;
- Consider that the system response time gets longer with longer sample transport lines;
- Build up pressure to flush sample pipes as turbulent as possible. If the process pressure is not high enough and/or cannot be guaranteed, then use sample pumps; for example a submersible pump for waste water;
- All wetted parts should be smooth and made of materials that are less sensitive for fouling. Plastics such as PVC and PE are sometimes preferable over Stainless Steel;
- Design the piping system without obstructions and reducing parts;
- Design a system without pockets or dead volumes;
- Keep the water flushing continuously;
- Calculate and use a correct inner diameter;
- If possible, use slope down and self emptying sample loops;
- Insulate and trace sample tubes/pipes in freezing conditions.
- For steam, condensate return water and boiler feed water applications (low ranges) use seamless SS pipes, 4 or 6 mm ID and keep the length as short as possible. The length of the pipe and the velocity in the pipe will dramatically effect the adsorption and memory phenomena.
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